Receiving device and automatic gain control method

ABSTRACT

A receiving device includes a receiver; a frequency converter; an A/D converter; and a digital signal processor, wherein the A/D converter includes a variable gain amplifier adjusting a signal level of the analog signal from the frequency converter; an A/D converting portion converting an analog signal from the variable gain amplifier into an m-bit digital signal and an n-bit digital signal and outputting the m-bit digital signal and the n-bit digital signal, the n-bit digital signal serving as an output signal to the digital signal processor; and a gain controller calculating a coarse adjustment gain of the variable gain amplifier on the basis of a power of the m-bit digital signal to control the gain of the variable gain amplifier and calculating a fine adjustment gain on the basis of a power of the n-bit digital signal to control the gain of the variable gain amplifier.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2005-333311, filed on Nov.17, 2005, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a receiving device and an automaticgain control method.

1. Related Art

In a conventional receiver, in order to keep the level of an inputsignal to an A/D converter constant, the level of the input signal isadjusted by using a variable gain amplifier. The gain of the variablegain amplifier is controlled depending on the level of a received signaland the level of an output signal from the A/D converter. This controlis called automatic gain control (AGC).

As a method of automatic gain control, a method obtained by combining afeedforward control method and a feedback control method is known (forexample Japanese Patent Publication Laid-open No. 10-56343 (p. 3 andFIG. 1) to be referred to as Patent Document 1 hereinafter).

In the automatic gain control method described in Patent Document 1, theRSSI(Received Signal Strength Indicator) of an analog received signalwhich has not been input to a variable gain amplifier is detected by aRSSI detector, and AGC coarse adjustment for controlling the gain of thevariable gain amplifier is performed on the basis of the RSSI(feedforward control). After the AGC coarse adjustment is performed, apower of a digital signal converted by the A/D converter is measured bya power measurement unit. On the basis of the measured power, AGC fineadjustment for controlling the gain of the variable gain amplifier isperformed (feedback control).

In this manner, according to the automatic gain control method describedin Patent Document 1, the automatic gain control is performed in twosteps of the AGC coarse adjustment and the AGC fine adjustment. For thisreason, control time can be made shorter than that in an automatic gaincontrol method which feedback control is performed a plurality of timeson the basis of the power of a digital signal serving as a result of A/Dconversion.

As described above, in the invention described in Patent Document 1,although automatic gain control can be increased in speed, a RSSIdetector must be additionally arranged to perform AGC coarse adjustment.For this reason, a circuit scale increases and a power consumptiondisadvantageously increase. In particular, since a mobile terminal orthe like requires a small size and a low power consumption, the problemof the circuit scale is serious for the mobile terminal or the like.

SUMMARY OF THE INVENTION

An advantage of an aspect of the present invention is to provide areceiver and an automatic gain control method which can be reduced insize and have low power dissipation.

A receiving device according to an embodiment of the present inventionincludes a receiver receiving a radio signal; a frequency converterconverting a frequency of an analog signal from the receiver; an A/Dconverter converting the analog signal into a digital signal; and adigital signal processor processing the digital signal to obtainreceived data, wherein the A/D converter includes: a variable gainamplifier adjusting a signal level of the analog signal; an A/Dconverting portion converting the analog signal from the variable gainamplifier into an m-bit digital signal and an n-bit (n>m) digital signaland outputting the m-bit digital signal and the n-bit digital signal,the n-bit digital signal serving as an output signal to the digitalsignal processor; and a gain controller calculating a coarse adjustmentgain of the variable gain amplifier on the basis of a power of the m-bitdigital signal to control the gain of the variable gain amplifier andcalculating a fine adjustment gain on the basis of a power of the n-bitdigital signal to control the gain of the variable gain amplifier.

A receiving device according to an embodiment of the present inventionincludes a receiver receiving a radio signal; a frequency converterconverting a frequency of an analog signal from the receiver; an A/Dconverter converting the analog signal into a digital signal; and adigital signal processor processing the digital signal to obtainreceived data, wherein the A/D converter includes: a variable gainamplifier adjusting a signal level of the analog signal from thefrequency converter; a quadrature detector separating a signal from thevariable gain amplifier to an in-phase component and an quadraturecomponent; a first low-pass filter removing higher harmonic wavesincluded in the in-phase component of the analog signal from thequadrature detector; a second low-pass filter removing higher harmonicwaves included in the quadrature component of the analog signal from thequadrature detector; a first A/D converting portion converting an analogsignal from the first low-pass filter into an m-bit digital signal ofthe in-phase component and an n-bit (n>m) digital signal of the in-phasecomponent and outputting the m-bit digital signal and the n-bit digitalsignal of the in-phase component,the n-bit digital signal of thein-phase component serving as an output signal to the digital signalprocessor; a second A/D converting portion converting an analog signalfrom the second low-pass filter into an m-bit digital signal of thequadrature component and an n-bit digital signal of the quadraturecomponent and outputting the m-bit digital signal and the n-bit digitalsignal of the quadrature component, the n-bit digital signal of thequadrature component serving as an output signal to the digital signalprocessor; a gain controller calculating a coarse adjustment gain of thevariable gain amplifier on the basis of a power of the m-bit digitalsignal of the in-phase component and the m-bit digital signal of thequadrature component to control the gain of the variable gain amplifierand calculating a fine adjustment gain on the basis of a power of then-bit digital signal of the in-phase component and the n-bit digitalsignal of the quadrature component to control the gain of the variablegain amplifier.

A receiving device according to an embodiment of the present inventionincludes a receiver receiving a radio signal; a frequency converterconverting a frequency of an analog signal from the receiver; an A/Dconverter converting the analog signal into a digital signal; and adigital signal processor processing the digital signal to obtainreceived data, wherein the A/D converter includes: a variable gainamplifier adjusting a signal level of the analog signal from thefrequency converter; a quadrature detector separating a signal from thevariable gain amplifier to an in-phase component and an quadraturecomponent; a first low-pass filter removing higher harmonic wavesincluded in the in-phase component of the analog signal from thequadrature detector; a second low-pass filter removing higher harmonicwaves included in the quadrature component of the analog signal from thequadrature detector; a first A/D converting portion converting an analogsignal from the first low-pass filter into an n-bit digital signal ofthe in-phase component, the n-bit digital signal of the in-phasecomponent serving as an output signal to the digital signal processor; asecond A/D converting portion converting an analog signal from thesecond low-pass filter into an n-bit digital signal of the quadraturecomponent, the n-bit digital signal of the quadrature component servingas an output signal to the digital signal processor; a first overflowdetector detecting whether the first A/D conversion portion is saturatedwhen the analog signal is input to the first A/D conversion portion; asecond overflow detector detecting whether the second A/D conversionportion is saturated when the analog signal is input to the second A/Dconversion portion; a gain controller calculating a coarse adjustmentgain which decreases a gain of the variable gain amplifier to controlthe gain of the variable gain amplifier when the first or the secondoverflow detector detects that the first or the second A/D conversionportion is saturated, and which, thereafter, calculating a fineadjustment gain obtained to control the gain of the variable gainamplifier by correcting the coarse adjustment gain on the basis ofpowers of the n-bit in-phase component digital signal and the n-bitquadrature component digital signal.

An automatic gain control method according to an embodiment of thepresent invention includes converting an input analog signal into anm-bit digital signal and an n-bit (n >m) digital signal serving as anoutput signal by using an A/D conversion potion; calculating a coarseadjustment gain of a variable gain amplifier on the basis of a power ofthe m-bit digital signal to adjust a signal level of the analog signalbefore the A/D conversion; and calculating a fine adjustment gain of thevariable gain amplifier on the basis of a power of the n-bit digitalsignal to adjust a signal level of the analog signal, the level of whichis adjusted in the calculation of the coarse adjustment gain.

An automatic gain control method according to an embodiment of thepresent invention includes converting an input analog signal into ann-bit digital signal serving as an output signal by using an A/Dconversion potion; detecting whether the A/D conversion portion isover-flowed when the analog signal inputted to the first A/D conversionportion; in a case that the A/D conversion portion is over-flowed,calculating a coarse adjustment gain of a variable gain amplifier toadjust a signal level of the analog signal before the A/D conversion;and calculating a fine adjustment gain of the variable gain amplifier onthe basis of a power of the n-bit digital signal to adjust a signallevel of the analog signal, the level of which is adjusted in thecalculation of the coarse adjustment gain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a receiveraccording to a first embodiment of the present embodiment;

FIG. 2 is a block diagram showing a configuration of an A/D converteraccording to a first embodiment of the present embodiment;

FIG. 3 is a block diagram showing a configuration of a 10-bits-pipelinedA/D converters an A/D converter according to a first embodiment of thepresent embodiment;

FIG. 4 is a diagram showing a wireless frame configuration according toa first embodiment of the present embodiment;

FIG. 5 is a flow chart showing an operation of an A/D converteraccording to a first embodiment of the present embodiment;

FIG. 6 is a block diagram showing a configuration of a receiveraccording to a second embodiment of the present embodiment;

FIG. 7 is a flow chart showing an operation of an A/D converteraccording to a second embodiment of the present embodiment;

FIG. 8 is a block diagram showing a configuration of a receiveraccording to a third embodiment of the present embodiment; and

FIG. 9 is a flow chart showing an operation of an A/D converteraccording to a third embodiment of the present embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the accompanying drawings.

FIRST EMBODIMENT

A schematic configuration of a receiver according to a first embodimentwill be described below with reference to FIG. 1.

The receiver shown in FIG. 1 includes an antenna 1 which receives ahigh-frequency radio signal, a low-noise amplifier (LNA) 2 whichamplifies a signal received by the antenna 1 with low noise, a frequencyconverter 3 which converts an output signal from the low-noise amplifier2 to an intermediate frequency signal, an A/D converter 4 which convertsa signal output from the frequency converter 3 from an analog signal toa digital signal, and a digital signal processor 5 which processes thedigital signal output from the A/D converter 4 to obtain receiving data.

The embodiment relates to automatic gain control executed by the A/Dconverter 4 of the receiver. Therefore, the configuration and theoperation of the receiver will be described below in detail withfocusing on the A/D converter 4.

The first embodiment will be described below with reference to FIGS. 2to 5.

FIG. 2 is a diagram showing the detailed configuration of the A/Dconverter 4 according to the first embodiment. The A/D converter 4 shownin FIG. 2 includes a band-pass filter 11 (to be referred to as a BPF 11hereinafter) for limiting a band, a variable gain amplifier 12 whichadjusts the signal level of a received IF signal which passes throughthe BPF 11, a quadrature detector 13 which separates the received IFsignal output from the variable gain amplifier 12 to in-phase componentsand quadrature components, low-pass filters 14 and 15 (to be referred toas LPFs 14 and 15 hereinafter) which remove higher harmonic wavesincluded in the components of the received IF signal output from thequadrature detector 13, and pipelined A/D converters 16 and 17 whichconvert the components from analog signals to digital signals, thecomponents being output from the LPFs 14 and 15 and the higher harmonicwaves are removed from the components. The pipelined A/D converters 16and 17 output 10-bit digital signals as final conversion results andoutput 6-bit digital signals as intermediate conversion results. Thedetails of the pipelined A/D converters 16 and 17 will be describedlater.

The A/D converter 4 further includes a power measurement unit 18 whichmeasures the power of the A/D-converted digital signal, a controller 19which controls the gain of the variable gain amplifier 12 on the basisof the power measured by the power measurement unit 18, and a D/Aconverter 20 which converts an output signal from the controller 19 froma digital signal to an analog signal to supply the analog signal to thevariable gain amplifier 12.

The detailed configurations of the pipelined A/D converters 16 and 17will be described below with reference to FIG. 3A and 3B.

The pipelined A/D converters 16 and 17 are arranged in units of thein-phase components and the quadrature components of the received IFsignal. However, since the pipelined A/D converters 16 and 17 havealmost the same configurations, the configuration of the pipelined A/Dconverter 16 which converts an in-phase component of the received IFsignal will be described below.

The pipelined A/D converter 16 includes a stage 161 constituted by astage K (K=0 to 9), a shift register group 162 obtained by connectingshift registers to each other in multistage to adjust the output timingsof digital signals output from the stages K of the stage 161, a 6-bitdigital correction logic 163 to which a 6-bit output signal ofprevious-stage from the shift register group 162 is provided, and a10-bit digital correction logic 164 to which output signals of all bitsfrom the shift register group 162 are supplied.

The stages K are sequentially connected in series with each other fromstage 9. When an analog signal from the LPF 14 is input to stage 9, thesignal is sequentially sent from stage 9 to stage 8, . . . , stage 0 bitby bit. Each of the stages K conduct 1-bit-quantization of the analogsignals from stage 9 to 0 according to clock timings, and it outputs thequantization results. Since the quantization results are output attimings at which quantization is performed at the stages K, the resultsare sequentially output from the stages 9 to 0 at 1-clock-intervals. Inorder to adjust the output timings of the quantization results, thequantization results are input to the shift register group 162.

In this case, the shift register group 162 is arranged to delay a 1-bitsignal by one clock. In order to adjust the output timing of thequantization result at stage 9 to the output timing of the quantizationresult at stage 0, nine shift registers (a1 to a9 in the shift registergroup 162) are connected in series with each other for stage 9.Similarly, eight shift registers (b1 to b8 in the shift register group162) are connected in series with each other for stage 8. Similarconfigurations are applied to the subsequent stages, respectively. Stage0 serving as the final stage is connected to the 10-bit digitalcorrection logic 164.

As described above, of the quantization results the output timings ofwhich are adjusted, the output results of stage 9 to stage 4 are inputto the 6-bit digital correction logic 163. After gain error correctionis performed on the output results by the 6-bit digital correction logic163, a 6-bit digital signal is output. Output results of stage 9 tostage 0 are input to the 10-bit digital correction logic 164. After gainerror correction is performed on the output results by the 10-bitdigital correction logic 164, a 10-bit digital signal is output.

At the stages K (K=0 to 9), an analog signal is quantized bit by bit.However, the analog signal may be quantized by a plurality of bits.Furthermore, a multi-bit shift operation may be performed by one shiftregister.

An operation of the A/D converter 4 will be described below withreference to FIGS. 4 to 5. A frame configuration of a wireless packetsignal obtained when the receiver according to the present invention isapplied to a wireless LAN serving as a wireless system will be explainedwith reference to FIG. 4, and the operation of the A/D converter 4 whenthe wireless packet signal is received will be explained with referenceto FIG. 5.

The upper side in FIG. 4 shows a frame configuration of a wirelesspacket signal in IEEE802.11a/g which is a standard for a wireless LAN.The wireless packet signal includes a preamble section (PR) 111 which isarranged at the start and used in automatic gain control, carrier/clockreproduction, or the like, a unique word section (UW) 112 used in framesynchronization, a signal section (SIG) 113 which transmits informationsuch as a transmission rate or a data length, and an information section(DATA) 114 which indicates data itself in the order named. Of thesesections, the preamble section 111 is constituted by a plurality ofsymbols, and some symbols (n symbols in this case) are used in automaticgain control.

The lower side in FIG. 4 shows the configuration of a part mainly usedin automatic gain control in the preamble section 111 for a wirelesspacket signal. The first and second symbols are apparatus responsesymbols 115 corresponding to response time until the A/D converter 4 isstarted. One symbol subsequent to the apparatus response symbol 115 isan AGC coarse adjustment symbol 116 used in AGC coarse adjustment. TheAGC coarse adjustment will be described later. One symbol subsequent tothe AGC coarse adjustment symbol 116 is a coarse adjustment responsesymbol 117. The coarse adjustment response symbol 117 corresponds toresponse time until a gain of the variable gain amplifier 12 becomesstable after the AGC coarse adjustment. n-5 symbols from the symbolsubsequent to the AGC coarse adjustment symbol 116 to symbol n-1 are AGCfine adjustment symbols 118 used in AGC fine adjustment. The AGC fineadjustment will be described later. The final symbol n is a fineadjustment response symbol 119 corresponding to response time until again of the variable gain amplifier 12 becomes stable after AGC fineadjustment.

An operation of the A/D converter 4 when the wireless packet signal isreceived will be described below with reference to the flow chart inFIG. 5.

When a received IF signal is input to the A/D converter 4, the A/Dconverter 4 takes the time, which is corresponds to the apparatusresponse symbol 115, to start. The input received IF signal passesthrough the BPF 11 for band limiting to be limited in a certainbandwidth (step 101).

The received IF signal passing through the BPF 11 is input to thevariable gain amplifier 12 and adjusted at a level corresponding to again set in the variable gain amplifier 12 (step 102). The received IFsignal amplified in the variable gain amplifier 12 is separated into anin-phase component and an quadrature component in the quadraturedetector 13. The in-phase component and the quadrature component passthrough the LPFs 14 and 15, respectively to remove higher harmonic wavesfrom the components (step 103). In this case, the in-phase component ofthe received IF signal passing through the LPF 14 is called an analog Isignal, and the quadrature component of the received IF signal passingthrough the LPF 15 is called an analog Q signal.

The analog I signal is input to the pipelined A/D converter 16, and theanalog Q signal is input to the pipelined A/D converter 17, so that theanalog I signal and the analog Q signal are converted into a digital Isignal and a digital Q signal, respectively. The digital I signal andthe digital Q signal which are input to the pipelined A/D converters 16and 17 to be firstly 6-bit-A/D-converted are output to the powermeasurement unit 18 as AGC coarse adjustment signals (step 104).

The power measurement unit 18 generates an AGC coarse adjustment powerobtained by converting the AGC coarse adjustment signal into a dB(decibel) value and outputs the AGC coarse power to the controller 19(step 105).

In the controller 19, on the basis of the AGC coarse adjustment powerand the optimum level of an input signal to an A/D converter, a firstgain at which the output from the variable gain amplifier 12 isestimated to have the optimum signal level is calculated. A coarse gaincontrol signal which designates the gain of the variable gain amplifier12 is generated and output to the D/A converter 20. Since the coarseadjustment gain control signal generated and output by the controller 19is a digital signal, the coarse adjustment gain control signal isconverted into an analog signal by the D/A converter 20, and the analogsignal is given to the variable gain amplifier 12 as a gain designationsignal (step 106).

Automatic gain control using the AGC coarse adjustment signal is calledAGC coarse adjustment, and is performed by using the AGC coarseadjustment symbol 116 shown in FIG. 4.

After the A/D converter 4 waits for time corresponding to the coarseadjustment response symbol 117 until gain designation performed by acoarse adjustment gain control signal is reflected on the variable gainamplifier 12, the A/D converter 4 performs AGC fine adjustment by usingthe AGC fine adjustment symbols 118 of the received IF signal. The AGCfine adjustment is executed as follows.

At first, the AGC fine adjustment symbols 118 are A/D-converted into a10-bit digital I signal and a 10-bit digital Q signal at the pipelinedA/D converters 16 and 17, respectively. The digital I signal and thedigital Q signal are output to the digital signal processor 5 connectedto the output of the A/D converter 4, and are input to the powermeasurement unit 18 as AGC fine adjustment signals, respectively. Thepower measurement unit 18 generates an AGC fine adjustment powerobtained by converting the AGC fine adjustment signals into dB (decibel)values and output to the controller 19 (step 107).

The controller 19 observes the fine adjustment powers input from thepower measurement unit 18 throughout a period in which the AGC fineadjustment symbols 118 are successive to calculate the average of thefine adjustment powers (step 108). Thereafter, on the basis of theaverage and the optimum level of the input signal to the A/D converter,a second gain at which an output from the variable gain amplifier 12 hasan optimum signal level is calculated, and a fine adjustment gaincontrol signal which designates the gain of the variable gain amplifier12 is generated and output to the D/A converter 20. Since the fineadjustment gain control signal generated and output by the controller 19is a digital signal, the digital signal is converted into an analogsignal by the D/A converter 20. The analog signal is applied to thevariable gain amplifier 12 as a gain designation signal (step 109).After the A/D converter 4 waits for time corresponding to the fineadjustment response symbol 119 until the gain designation obtained bythe fine adjustment gain control signal is reflected on the variablegain amplifier 12, the remaining wireless frame subsequent to the fineadjustment response symbol 119 is A/D-converted.

In this case, the gain of the variable gain amplifier 12 calculated bythe controller 19 may be set such that outputs from the pipelined A/Dconverters 16 and 17 are not saturated, for example, the amplitudes ofthe signals input to the pipelined A/D converters 16 and 17 are about ¼to ½ of the full scale.

Furthermore, the saturation level may be lowered to set the gain suchthat a desired dynamic range is satisfied.

As described above, according to the first embodiment, AGC coarseadjustment of the variable gain amplifier 12 is performed by usingintermediate results of conversion in the pipelined A/D converters 16and 17, so that a RSSI detector need not be additionally arranged forAGC coarse adjustment, and further the pipelined A/D converters 16 and17 which can output the intermediate results can be realized in almostthe same scale of circuit as that of a conventional pipelined A/Dconverter. For this reason, a reduction in circuit scale and a reductionin power consumption can be achieved. Since a signal input to or outputfrom the power measurement unit 18 is a digital signal, information,which is more stable than information obtained by converting the RSSI ofan analog signal into a digital signal, can be supplied to thecontroller 19. In addition, since automatic gain control is performed intwo steps, the control can be performed at a high speed. In this manner,a preamble signal for automatic gain control can be shortened, andpreamble signals for time synchronization or frequency synchronizationcan be longly assured. That is, a ratio of other signals to a packetlength can be increased.

SECOND EMBODIMENT

A second embodiment of the present invention will be described belowwith reference to FIGS. 6 and 7. FIG. 6 is a diagram of an A/D converter4 according to the second embodiment. The same reference numerals as inthe A/D converter 4 shown in FIG. 2 denote the same parts in theconfiguration of the A/D converter 4 according to the second embodiment,and a description thereof will be omitted.

The A/D converter 4 according to the second embodiment includes 6-bitflash A/D converters 21 and 22 and 10-bit pipelined A/D converters 23and 24. The 6-bit flash A/D converters 21 and 22 output 6-bit A/Dconversion results corresponding to input signals from LPFs 14 and 15 tothe power measurement unit 18. The 10-bit pipelined A/D converters 23and 24 do not output intermediate results of A/D conversion of the inputsignals from the LPFs 14 and 15. Unlike the pipelined A/D converters 6and 7 shown in FIG. 2, the 10-bit pipelined A/D converters 23 and 24output only the 10-bit A/D conversion results to the digital signalprocessor 5 and the power measurement unit 18 following to the outputsof the 10-bit pipelined A/D converters 23 and 24.

Since a frame configuration of a wireless packet signal received by thereceiver according to the embodiment is the same as the configuration ofthe first embodiment, a description thereof will be omitted.

An operation of the A/D converter 4 according to the second embodiment,when the wireless packet signal is received, will be described belowwith reference to FIG. 7. The same reference numerals as in FIG. 5denote the same steps in FIG. 7, and a description thereof will beomitted.

The received signal, as in the first embodiment, is separated into ananalog I signal and an analog Q signal (step 101 to step 103).Thereafter, the analog I signal is input to the 6-bit flash A/Dconverter 21 and the 10-bit pipelined A/D converter 23, and the analog Qsignal is input to the 6-bit flash A/D converter 22 and the 10-bitpipelined A/D converter 24. The analog I signal and the analog Q signalinput to the 6-bit flash A/D converters 21 and 22 are converted into a6-bit digital I signal and a 6-bit digital Q signal. The 6-bit digital Isignal and the 6-bit digital Q signal are output to the powermeasurement unit 18 as AGC coarse adjustment signals (step 110). Afterthe input, as in the first embodiment, AGC coarse adjustment isperformed on the variable gain amplifier 12 (step 105 and step 106).

Thereafter, the digital I signal and the digital Q signal converted bythe 10-bit pipelined A/D converters 23 and 24 are output to the digitalsignal processor 5 and output to the power measurement unit 18 as AGCfine adjustment signals (step 111). After the input, as in the firstembodiment, AGC fine adjustment is performed on the variable gainamplifier 12 (step 108 and step 109).

As described above, according to the second embodiment, the AGC coarseadjustment of the variable gain amplifier 12 is performed by using theoutputs from the 6-bit flash A/D converters 21 and 22, so that a RSSIdetector need not be additionally prepared for AGC coarse adjustment.For this reason, a reduction in circuit scale and a reduction in powerconsumption can be achieved. Since signals input to or output from thepower measurement unit 18 are digital signals, information which is morestable than information obtained by converting the RSSI of an analogsignal into a digital signal can be supplied to the controller 19. Inaddition, since automatic gain control is performed in two steps, thecontrol can be performed at a high speed. In this manner, a preamblesignal for automatic gain control can be shortened, and preamble signalsfor time synchronization or frequency synchronization can be longlyassured. That is, a ratio of other signals to a packet length can beincreased.

THIRD EMBODIMENT

The third embodiment of the present invention will be described belowwith reference to FIGS. 8 and 9. FIG. 8 is a diagram of an A/D converter4 according to the third embodiment. The same reference numerals as inthe A/D converter 4 shown in FIG. 2 denote the same parts in theconfiguration of the A/D converter 4 according to the third embodiment,and a description thereof will be omitted.

The A/D converter 4 according to the third embodiment has overflowdetectors 25 and 26 in place of the 6-bit flash A/D converters 21 and 22in the A/D converter 4 according to the second embodiment. The overflowdetectors 25 and 26 detect whether input signals to 10-bit pipelined A/Dconverters 23 and 24 are saturated, and the overflow detectors 25 and 26output the detection results to the controller 19.

Since the frame configuration of the wireless packet signal received bythe receiver according to the third embodiment is the same as theconfiguration in the first embodiment, a description thereof will beomitted.

An operation of the A/D converter 4 according to the third embodiment,when a signal constituted by the wireless frame is received, will bedescribed below with reference to FIG. 9. The same reference numerals asin FIG. 5 denote steps which perform the same operations in FIG. 9, anda description thereof will be omitted.

The received signal is separated into an analog I signal and an analog Qsignal (step 101 to step 103). Thereafter, the analog I signal and theanalog Q signal are input to 10-bit pipelined A/D converters 23 and 24,respectively. At this time, the overflow detectors 25 and 26 detectwhether the input signals to the 10-bit pipelined A/D converters 23 and24 are saturated, and output the detection results to a controller 19(step 112).

When the overflow detectors 25 and 26 detect that the input signals tothe 10-bit pipelined A/D converters 23 and 24 are saturated, thecontroller 19 generates a coarse adjustment gain control signal (to bereferred to as a coarse adjustment signal hereinafter) which designatesthe variable gain amplifier 12 to decrease the gain of the variable gainamplifier 12, and outputs the coarse adjustment signal to a D/Aconverter 20. Since the coarse adjustment signal generated and output bythe controller 19 is a digital signal, the digital signal is convertedinto analog signal by a D/A converter 20 to give a gain designation tothe variable gain amplifier 12 (step 113). However, when it is detectedthat the input signals are not saturated, the controller 19 does notchange the gain of the variable gain amplifier 12.

The 10-bit digital I signal and the 10-bit digital Q signal converted bythe 10-bit pipelined A/D converters 23 and 24 are output to the digitalsignal processor 5 and output to the power measurement unit 18 as AGCfine adjustment signals (step 114). After the input, as in the firstembodiment, AGC fine adjustment is performed on the variable gainamplifier 12 (step 108 and step 109).

As described above, according to the third embodiment, when the overflowdetectors 25 and 26 detect that input signals to the 10-bit pipelinedA/D converters 23 and 24 are saturated, AGC coarse adjustment of thevariable gain amplifier 12 is performed, so that a RSSI detector neednot be additionally prepared for AGC coarse adjustment. For this reason,a reduction in circuit scale and a reduction in power consumption can beachieved. Since signals input to or output from the power measurementunit 18 are digital signals, information which is more stable thaninformation obtained by converting the RSSI of an analog signal into adigital signal can be supplied to the controller 19. In addition, sinceautomatic gain control is performed in two steps, the control can beperformed at a high speed. In this manner, a preamble signal forautomatic gain control can be shortened, and preamble signals for timesynchronization or frequency synchronization can be longly assured. Thatis, a ratio of other signals to a packet length can be increased.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A receiving device comprising: a receiver receiving a radio signal; afrequency converter converting a frequency of an analog signal from thereceiver; an A/D converter converting the analog signal into a digitalsignal; and a digital signal processor processing the digital signal toobtain received data, wherein the A/D converter includes: a variablegain amplifier adjusting a signal level of the analog signal; an A/Dconverting portion converting the analog signal from the variable gainamplifier into an m-bit digital signal and an n-bit (n>m) digital signaland outputting the m-bit digital signal and the n-bit digital signal,the n-bit digital signal serving as an output signal to the digitalsignal processor; and a gain controller calculating a coarse adjustmentgain of the variable gain amplifier on the basis of a power of the m-bitdigital signal to control the gain of the variable gain amplifier andcalculating a fine adjustment gain on the basis of a power of the n-bitdigital signal to control the gain of the variable gain amplifier. 2.The receiver according to claim 1, wherein the A/D conversion portion isan n-bit pipelined A/D converter, the m-bit digital signal is ahigher-order m-bit of the conversion output signal converted by then-bit pipelined A/D converter, and the n-bit digital signal is anall-bit of the conversion signal converted by the n-bit pipelined A/Dconverter.
 3. The receiver according to claim 1, wherein amplitudes ofsignals inputted to the A/D converting portion are about ¼ to ½ of anamplitude of signal inputted to the A/D converting portion andsaturating the A/D converting portion.
 4. The receiver according toclaim 2, wherein amplitudes of signals inputted to the A/D convertingportion are about ¼ to ½ of an amplitude of signal inputted to the A/Dconverting portion and saturating the A/D converting portion.
 5. Areceiving device comprising: a receiver receiving a radio signal; afrequency converter converting a frequency of an analog signal from thereceiver; an A/D converter converting the analog signal into a digitalsignal; and a digital signal processor processing the digital signal toobtain received data, wherein the A/D converter includes: a variablegain amplifier adjusting a signal level of the analog signal from thefrequency converter; a quadrature detector separating a signal from thevariable gain amplifier to an in-phase component and an quadraturecomponent; a first low-pass filter removing higher harmonic wavesincluded in the in-phase component of the analog signal from thequadrature detector; a second low-pass filter removing higher harmonicwaves included in the quadrature component of the analog signal from thequadrature detector; a first A/D converting portion converting an analogsignal from the first low-pass filter into an m-bit digital signal ofthe in-phase component and an n-bit (n>m) digital signal of the in-phasecomponent and outputting the m-bit digital signal and the n-bit digitalsignal of the in-phase component, the n-bit digital signal of thein-phase component serving as an output signal to the digital signalprocessor; a second A/D converting portion converting an analog signalfrom the second low-pass filter into an m-bit digital signal of thequadrature component and an n-bit digital signal of the quadraturecomponent and outputting the m-bit digital signal and the n-bit digitalsignal of the quadrature component, the n-bit digital signal of thequadrature component serving as an output signal to the digital signalprocessor; a gain controller calculating a coarse adjustment gain of thevariable gain amplifier on the basis of a power of the m-bit digitalsignal of the in-phase component and the m-bit digital signal of thequadrature component to control the gain of the variable gain amplifierand calculating a fine adjustment gain on the basis of a power of then-bit digital signal of the in-phase component and the n-bit digitalsignal of the quadrature component to control the gain of the variablegain amplifier.
 6. The receiver according to claim 5, wherein the firstand the second A/D conversion portions are n-bit pipelined A/Dconverters, the m-bit digital signal is an higher-order m-bit of theconversion output signal converted by the n-bit pipelined A/D converter,and the n-bit digital signal is an all-bit conversion signal convertedby the n-bit pipelined A/D converter.
 7. The receiver according to claim5, wherein the first A/D conversion portion includes a first in-phaseA/D converter generating and outputting the m-bit /in-phase componentdigital signal and a second in-phase A/D converter generating andoutputting the n-bit in-phase component digital signal, and a second A/Dconverter includes a first quadrature A/D converter generating andoutputting the m-bit quadrature component digital signal and a secondquadrature A/D converter generating and outputting the n-bit quadraturecomponent digital signal.
 8. The receiver according to claim 6, whereinthe first A/D conversion portion includes a first in-phase A/D convertergenerating and outputting the m-bit in-phase component digital signaland a second in-phase A/D converter generating and outputting the n-bitin-phase component digital signal, and a second A/D converter includes afirst quadrature A/D converter generating and outputting the m-bitquadrature component digital signal and a second quadrature A/Dconverter generating and outputting the n-bit quadrature componentdigital signal.
 9. The receiver according to claim 6, wherein the firstin-phase A/D converter and the first quadrature A/D converter are flashA/D converters, and the second in-phase A/D converter and the secondquadrature A/D converter are pipelined A/D converters.
 10. The receiveraccording to claim 5, wherein amplitudes of signals inputted to thefirst and second A/D converting portion are about ¼ to ½ of an amplitudeof signal inputted to the A/D converting portion and saturating the A/Dconverting portion.
 11. The receiver according to claim 6, whereinamplitudes of signals inputted to the first and second A/D convertingportion are about ¼ to ½ of an amplitude of signal inputted to the A/Dconverting portion and saturating the A/D converting portion.
 12. Areceiving device comprising: a receiver receiving a radio signal; afrequency converter converting a frequency of an analog signal from thereceiver; an A/D converter converting the analog signal into a digitalsignal; and a digital signal processor processing the digital signal toobtain received data, wherein the A/D converter includes: a variablegain amplifier adjusting a signal level of the analog signal from thefrequency converter; a quadrature detector separating a signal from thevariable gain amplifier to an in-phase component and an quadraturecomponent; a first low-pass filter removing higher harmonic wavesincluded in the in-phase component of the analog signal from thequadrature detector; a second low-pass filter removing higher harmonicwaves included in the quadrature component of the analog signal from thequadrature detector; a first A/D converting portion converting an analogsignal from the first low-pass filter into an n-bit digital signal ofthe in-phase component, the n-bit digital signal of the in-phasecomponent serving as an output signal to the digital signal processor; asecond A/D converting portion converting an analog signal from thesecond low-pass filter into an n-bit digital signal of the quadraturecomponent, the n-bit digital signal of the quadrature component servingas an output signal to the digital signal processor; a first overflowdetector detecting whether the first A/D conversion portion is saturatedwhen the analog signal is input to the first A/D conversion portion; asecond overflow detector detecting whether the second A/D conversionportion is saturated when the analog signal is input to the second A/Dconversion portion; a gain controller calculating a coarse adjustmentgain which decreases a gain of the variable gain amplifier to controlthe gain of the variable gain amplifier when the first or the secondoverflow detector detects that the first or the second A/D conversionportion is saturated, and which, thereafter, calculating a fineadjustment gain obtained to control the gain of the variable gainamplifier by correcting the coarse adjustment gain on the basis ofpowers of the n-bit in-phase component digital signal and the n-bitquadrature component digital signal.
 13. The receiver according to claim12, wherein the first and the second A/D conversion portions arepipelined A/D converters.
 14. The receiver according to claim 12,wherein the first and the second A/ID conversion portions are n-bitpipelined A/D converters, the m-bit digital signal is a higher-orderm-bit of the conversion output signal converted by the n-bit pipelinedA/D converter, and the n-bit digital signal is an all-bit of theconversion signal converted by the n-bit pipelined A/D converter. 15.The receiver according to claim 12, wherein the first and the second A/Dconversion portion are n-bit pipelined A/D converters, the m-bit digitalsignal is a higher-order m-bit of the conversion output signal convertedby the n-bit pipelined A/D converter, and the n-bit digital signal is anall-bit of the conversion signal converted by the n-bit pipelined A/Dconverter.
 16. The receiver according to claim 12, wherein amplitudes ofsignals inputted to the first and the second A/D converting portion areabout ¼ to ½ of an amplitude of signal inputted to the first and thesecond A/D converting portion and saturating the first and the secondA/D converting portion.
 17. The receiver according to claim 13, whereinamplitudes of signals inputted to the first and the second A/Dconverting portion are about ¼ to ½ of an amplitude of signal inputtedto the first and the second A/D converting portion and saturating thefirst and the second A/D converting portion.
 18. An automatic gaincontrol method comprising: converting an input analog signal into anm-bit digital signal and an n-bit (n>m) digital signal serving as anoutput signal by using an A/D conversion potion; calculating a coarseadjustment gain of a variable gain amplifier on the basis of a power ofthe m-bit digital signal to adjust a signal level of the analog signalbefore the A/D conversion; and calculating a fine adjustment gain of thevariable gain amplifier on the basis of a power of the n-bit digitalsignal to adjust a signal level of the analog signal, the level of whichis adjusted in the calculation of the coarse adjustment gain.
 19. Theautomatic gain control method according to claim 18, wherein the m-bitdigital signal is a higher-order m-bit of the conversion signalconverted by A/D conversion portion, the n-bit digital signal is anall-bit of the conversion signal converted by A/D conversion portion.20. An automatic gain control method comprising: converting an inputanalog signal into an n-bit digital signal serving as an output signalby using an A/D conversion potion; detecting whether the A/D conversionportion is over-flowed when the analog signal inputted to the first A/Dconversion portion; in a case that the A/D conversion portion isover-flowed, calculating a coarse adjustment gain of a variable gainamplifier to adjust a signal level of the analog signal before the A/Dconversion; and calculating a fine adjustment gain of the variable gainamplifier on the basis of a power of the n-bit digital signal to adjusta signal level of the analog signal, the level of which is adjusted inthe calculation of the coarse adjustment gain.